Firstly, many thanks for helping. However, I've managed now to get it to connect - I used super grok to help get to the steps necessary, and now it's all good. Thanks again though.
For info, this was grok's advice:
The Google Nest Learning Thermostat identifies and communicates with its specific Heat Link (the device that controls the boiler) via a proprietary wireless protocol (similar to Thread), operating over a range of up to about 30 meters. This connection is distinct from the thermostat's Wi-Fi connection to your router and the internet. The pairing ensures secure, dedicated communication between one thermostat and one Heat Link—each Heat Link can only pair with a single thermostat display, and vice versa.
--- How Pairing Works and Identification Occurs
- Pre-Paired for New Installations: When you purchase a new Nest Learning Thermostat kit, the thermostat and its accompanying Heat Link are typically pre-paired at the factory. During initial setup (guided by the Nest app or the thermostat's on-screen prompts), the thermostat automatically recognizes and connects to its matched Heat Link without needing additional steps like entering codes.
- Unique Identification: Each Heat Link has a unique 6-character pairing code printed on a label at the bottom of its case. This code acts as an identifier, allowing the thermostat to distinguish and securely connect to the correct Heat Link. The thermostat stores this pairing information locally.
- In Homes with Multiple Units: With three thermostats and Heat Links like yours, each pair operates independently using its own unique code and wireless channel. As long as they are set up one at a time and within range, there's no cross-talk or interference—the system doesn't rely on broadcasting to all devices but on the specific paired connection. If multiple Heat Links are in range during pairing, entering the exact code ensures the thermostat links to the intended one.
- Manual Pairing Process (for Replacements or Reconnects): If the connection is lost or you're replacing components, manual pairing is required. This involves resetting the Heat Link to factory defaults (putting it into discoverable/pairing mode) and entering the code on the thermostat. The process is local and doesn't require internet, though the thermostat may need Wi-Fi for full app integration later.
--- Resolving Your Connection Issue
Google's advice to simply swap the thermostat assumes the replacement is pre-configured or that the pairing persists, but in practice (especially for just the display unit), the new thermostat often won't automatically recognize the existing Heat Link. Based on official guidance and user reports, you'll likely need to manually re-pair them. Here's how:
1. Gather the Pairing Code: Remove the cover from your existing Heat Link and note the 6-character code on the label at the bottom.
2. Prepare the Devices: Ensure the new thermostat is powered on, connected to its base, and has a battery level above 3.8V (check via Settings > Technical Info > Power). Bring the thermostat close to the Heat Link (ideally in the same room) to avoid range issues.
3. Reset the Heat Link: Press and hold the button on the Heat Link for about 45 seconds until the light starts pulsing blue slowly. Release, wait 5 seconds, then repeat the hold for another 45 seconds. This performs a factory reset and puts it into pairing mode (pulsing blue light).
4. Pair on the Thermostat: On the new thermostat's display, navigate to Settings (gear icon) > Nest app (or similar setup option) > Add product or Replace Heat Link (even though you're not replacing the Heat Link—this option triggers the pairing flow). Enter the 6-digit code when prompted, then select Connect. Wait up to a minute for the "Heat Link connected wirelessly" message. The Heat Link's light should turn solid green if successful.
5. Test the Connection: Increase the temperature on the thermostat to see if heating activates (the Heat Link light should turn green). If it shows an H71 error (disconnected Heat Link), repeat the steps or check for interference (e.g., thick walls, distance, or other wireless devices).
6. If Wired Option is Available: As a temporary workaround, you can connect the thermostat directly to the Heat Link using wires to the T1 and T2 terminals (if your setup allows), but this isn't ideal for wireless operation.
If these steps don't work, remove the old (broken) thermostat from the Nest/Google Home app first, then add the new one. For further troubleshooting, contact Google Nest support—they may provide a replacement Heat Link if the issue persists. Professional installation is recommended if you're uncomfortable with wiring or resets.
